Refine and speedup momentum operator.

[Profiling]  Update elementwise op

fix typo in pip_install_cn/en.rst

Update write docs cn

Change the instructions to use https instead of SSH

use awk command to replace bc

* Add DataFeeder

A v2 API like data feeder for book demos.
We can feed data directly from reader.

* Fix CI

* Add an unittest for while/rnn op forward

* Add unittest for raw while op backward

* Fix CI

* add doc config for fluid

* fix typo

* follow comments

Make lstm_op follow google code style.

add WITH_DOC for print_operators_doc

* Add DataFeeder

A v2 API like data feeder for book demos.
We can feed data directly from reader.

* Fix CI

* Remove batch_size_dim for feeder

Also add __all__ to data_feeder.py

* Follow comment

simplify the CMakeLists.txt of trainer/tests and gserver/tests

Fix the doc of LSTM operator.

* Add hinge loss op

* Update hinge-loss equation for proper latex

Simple pipe reader for hdfs or other service

Merge branch 'print_operators_doc' of https://github.com/luotao1/Paddle into luotao1-print_operators_doc

polish mkldnn doc

Fix the compiling error when seting WITH_C_API=ON and WITH_PYTHON=ON.

Add switch for distributed support